Respiratory effects

major cause of mortality and morbiditythermal injury in a closed environment may cause pulmonary inhalation injury
and intoxication from combustion products. Of these most important are
carbon
monoxide and cyanide

Airway injury

upper airway damage is due to heat

upper and middle airway damage due to inhalation of hot particles or noxious
chemicals or direct flame injury

maximal oedema formation at about 24h but depends on a variety of factors
including adequacy of resuscitation

Lung injury

pathophysiology of parenchymal lung damage not known. ? due to direct
thermal injury and chemical injury. ? due to indirect effects such as fluid
overload, secondary infection, ARDS, PE

steam is only agent that results in immediate injury to lung parenchyma

impairment of gas exchange due to V:Q mismatch due to airway injury rather
than alveolar injury

lung complications can occur following major burns without inhalation injury

acidosis develops within hours after > 30% burns. Has both metabolic and
respiratory components. Former due to products of heat-damaged tissues and
relative hypoxia

some evidence to suggest that stress response can be modulated and reduced if enteral feeding is started in first 24 h

Immunological changes

immune and inflammatory response depressed in severe burn injuries

sepsis accounts for >50% of mortality in burns

Haematological

red cell loss due to haemolysis and intravascular coagulation likely in
patients with >20% burns. May be as high as 1% of red cell mass per % of full
thickness burn. Red cell extravasation also occurs

increase in red cell destruction thought to be due to some factor in plasma
which makes red cells more liable to destruction

coagulopathy may occur during resuscitation phase due to dilution and
consumption

DIC common in extensive burns

hypercoagulable state may develop 2-4 weeks post burn

Others

oliguric/non-oliguric renal failure may occur due to renal hypoperfusion,
haemoglobinuria, myoglobinuria or sepsis. Associated with high mortality even
with dialysis

stress ulceration in 11% of burn patients

Classification

- : only involves epithelial layer. Often very painful but
resolves with no residual scarring. Skin is red and painful but blisters are not
present
- second degree: involves epithelium and part of dermis. Pain and scarring vary
according to depth of burn. In superficial second-degree burns damage is limited
to epidermis and uppermost part of dermis. Deep second-degree burns spare only
the deepest portion of dermis
- : full thickness. Usually painless due to destruction of cutaneous
innervation. Leads to scarring. Usually dry and have milky white or tanned
leather appearance

As for superficial partial thickness burns. Wound excision and grafting
at earliest feasible time. For £ 25% burns
should be enough donor site to close all wounds at the same operation. For
more extensive burns: staged excision and closure or complete excision and
temporary skin substitute to cover areas remaining after all available
autologous skin has been harvested and grafted

# Can also be treated effectively by covering the denuded wound with skin
allograft or xenograft or a commercially available synthetic membrane. If
adherent these reduce pain and eliminate the need for dressing changes.

Assessment and initial management

Take a primary and secondary survey approach to assessment, starting by
looking for and treating life threatening problems before going on to a more
thorough assessment. Remember that burns may be associated with significant
trauma

Primary survey

Check airway patency

if there are signs of airway obstruction remember that the airway
may be burnt and oedematous and intubation may be difficult. Obtain
expert help if you are not experienced in managing difficult intubations

Chemical burns: flush with copious amounts of water for 15-30 min,
avoiding contamination of healthy skin. Do not attempt to neutralize the
chemical agent

Secondary survey

Obtain a brief history of the mechanism of the burn

fire in enclosed space is associated with greater risk of carbon
monoxide or cyanide poisoning

explosions associated with risk of trauma secondary to blast injury

Assess for extent and depth of burn. At this stage it is difficult to
distinguish between superficial and deep second degree burn.

first degree
burn is characterized by erythema of the skin, without blistering

third degree
burn is leathery and inelastic with a wrinkled appearance over bony
prominences. It is not perfused and has a milky appearance with no
capillary refill unless the subcutaneous fat has also been burned in
which case the wound looks brown. Note that these appearances may not be
evident until the dead superficial skin (brown in colour) has been
removed

all other burned areas are second degree burns

extent of burn can be assessed using a Lund-Browder chart

in the absence of a chart it can be calculated in adults using
the rule of nines: each arm 9%, each leg 18%, each side of
trunk 18%, head 9% and perineum 1%. Age adjusted approximations available for
assessing burn size in children

Check for circumferential burns of neck, trunk or limbs which may
require urgent escharotomy

urgent escharotomy may be required for extensive burns to trunk
(even if not completely circumferential) if there is difficulty
ventilating the patient or if abdominal compartment syndrome is
impairing circulation

check capillary refill of digits to assess limb circulation.
Impaired limb circulation in the presence of circumferential burns is an
indication for urgent escharotomy

Fluid resuscitation

- IV fluids if burn >20% or 15% with inhalation injury
- disagreement regarding quantity and choice of fluids
- larger volumes should be given in first 8-12 h when fluid loss is greatest
with gradual reduction over next 16h. Patients with inhalational injuries
frequently require up to 50% more fluid to be resuscitated adequately during the
first 24 h. (NB amount of lung water appears to be higher in patients who are
under-resuscitated than those who are fully resuscitated)
- Parkland formula: 4 ml/kg/% burn of Ringer's solution during first 24 h with
one half given in first 8 h
- sodium requirement 0.5 mmol/kg/% burn
- recommended regimes should be titrated to individual requirements. Frequent
monitoring of patient response and biochemical investigations are necessary to
adjust fluid regime. Aim for urine output >0.5 ml/kg in adults and > 1
ml/kg in children <25 kg in the absence of rhabdomyolysis. Fluid regimes
which result in appreciably higher urine outputs increase wound oedema and may
necessitate otherwise unneeded escharotomies
- blood transfusion indicated in patients with massive haemolysis or blood loss
- mannitol to maintain urine output of 1-2 ml/kg/hr if haemolysis or muscle
damage significant to prevent renal failure secondary to haem proteins or
rhabdomyolysis
- use of colloid for resuscitation has decreased mainly because controlled
trials have shown no clear advantage to its use and one showed potentially
harmful effects: increased accumulation of water in lungs and an increased rate
of clinical pulmonary complications associated with use of albumin
- beyond 24 h: increased permeability to protein (but not Na) has largely
returned to normal and thus thought that colloid should be used for
resuscitation. However this practice may be harmful: administration of albumin
to patients in stable condition after 24 h of clinically satisfactory
crystalloid resuscitation led to a significant decrease in GFR below the normal
range despite an increase in plasma volume. Also important to give water
(dextrose) due to high evaporative loss from skin. High K requirement due to
shift of K from ECF to ICF as injured cells recover

Respiration

- may be no respiratory symptoms in first 24h
- careful assessment of airway with immediate intubation if any doubt with
regard to patency exists. UAO may develop suddenly and catastrophically.
- other indications for intubation:

stridor

circumferential burns of neck

facial burns

full thickness burns of nose or lips

oedema of pharynx or larynx

unconsciousness

loss of airway reflexes

carbon monoxide or cyanide poisoning

any signs of respiratory distress

> 40% burns due to risk of laryngeal oedema as part of generalised
oedema that occurs with large BSA burns. (May be necessary for 25-40% burns.
Usually unnecessary < 25%)

- use largest ETT possible to facilitate lung toilet +/- bronchoscopy
- humidification particularly important in those with lower airway burns
- tracheostomy occasionally required on presentation because of facial and upper
airway burns
- avoid suxamethonium: may result in severe hyperkalaemia 2-60 days following
burn
- burn patients relatively insensitive to non-depolarizing drugs and may require
large doses for paralysis
- burn or soot around mouth or nose should increase suspicion of an inhalational
burn. Any patient burned in a closed space where smoke can accumulate should be
treated as having a smoke inhalation injury
- lungs particularly sensitive to barotrauma. HFV and permissive hypercapnia
have been advocated to reduce complications
- suspect carbon monoxide poisoning if patients show signs of mental disturbance
- minority of patients will require bronchodilators for smoke-induced irritation
of airways

Nutritional support

- commence when resuscitative phase is complete
- enteral preferable
- requirements of burn patients not significantly different from those of other
trauma victims
- additional protein may improve immune function and mortality
- formulations with high protein, low fat and linoleic acid, but enriched
vitamins A & C, zinc, histidine, cysteine, arginine and omega 3 fatty acids
said to be superior to standard regimes

Sepsis

- skin and lungs are most common sources of infection
- diagnosis of sepsis may be difficult
- signs of burn wound sepsis:

focal or diffuse areas of discolouration (black, brown or violet)

purulent fluid from eschar

signs of cellulitis at unburned margins of burn wound

too rapid eschar separation

- general signs of sepsis in burned patients include:

change in sensorium

development of ileus

development of glucose intolerance

Specific treatment of burn

- early excision and grafting minimizes infection, hastens wound healing,
reduces blood loss and improves survival
- only after fluid resuscitation and when patient's condition is stable, usually
24-36 hrs post burn
- mortality high in patients at extremes of age and with > 60% burns
- best wound coverage is split thickness autografts but donor sites limited and
there is associated morbidity
- allogeneic skin grafts have problems of availability and disease transmission
- topical antimicrobial therapy after wound cleaning and deroofing of blisters
may lower infection rate but is not of itself the treatment of choice. Silver
sulphadiazine 1% is agent most commonly used. May cause dermal hypersensitivity
reactions and transient leucopaenia in up to 5%. Latter is due, in part, to
marrow toxicity. Nearly always resolves within a period of several days despite
continuation of drug.
- other agents include: